The invention relates to a connector between a reaction pipe of a reaction furnace and a cooling pipe of a reaction gas cooler, as well as to a method for connecting a reaction pipe of a reaction furnace to a cooling pipe of a reaction gas cooler, wherein the cooling pipe is embodied as a double pipe having an inner pipe and an outer pipe, wherein the inner pipe is disposed in an extension of the reaction pipe and the outer pipe surrounds the inner pipe such as to form an intermediate cooling space between them.
Pyrolysis or ethylene reaction furnaces form, within the ethylene unit, the heating element for the production of the base materials ethylene, propylene, butadiene, etc. for the plastics industry.
Saturated hydrocarbons, primarily ethane, propane, butane, LNG, naphtha and oil gas are used as starting materials. The conversion of the saturated hydrocarbons into the unsaturated hydrocarbons takes place in the reaction pipe at inlet temperatures of 500-680° C. and outlet temperatures of 775-875° C., and in a pressure range of 1.5-5 bar.
In downstream reaction gas coolers at the furnace discharge, the unsaturated hydrocarbons (also known as reaction gases) are cooled off from 775-875° C. to about 350-450° C. accompanied by the formation of high or low pressure vapor. The “cooling water” has a boiling or distillation temperature at an appropriate pressure. The cooling takes place due to the phase transition from liquid to vapor.
The reaction gas cooler is composed of one or more double pipes, whereby the reaction gas that is to be cooled off is disposed in the inner pipe, and the cooling water is disposed in the outer pipe, in other words, about the inner pipe. Depending on the type of furnace, the reaction gas can enter the reaction gas cooler from below and flow upwardly, or can enter from above and flow downwardly.
The cooled double pipe of the reaction gas cooler is connected by a special transition piece with the reaction pipe that extends out of the reaction furnace. This transition piece is either cooled with vapor, or is designed as an uncooled component that is filled with heat-insulating material. Such an uncooled transition piece is known from DE 39 10 630 C3, and is comprised of an expanded, fork-shaped tube end having an inner section and an outer section. The space present between the two sections is filled with a heat-insulating material. Merely the outer section of the transition piece is connected to the reaction gas cooler, while a play is maintained in the radial and axial directions between the inner section of the transition piece and the cooling pipe of the reaction gas cooler.
The uncooled transition piece known from DE 39 10 630 C3 has the advantage relative to the cooled transition piece that at the point of connection the wall temperatures are nearly the same, thus avoiding thermal stresses. Despite this clear advantage, in older reaction gas units cooled transition pieces are still in use. There is a need in existing reaction gas units to replace the exiting cooled transition pieces with uncooled transition pieces.
A single-tube heat exchanger for the cooling of reaction gas is known from EP 718 579 B1 and EP 810 414 B1; it is provided with a special supply chamber for the coolant. The supply chamber is comprised of individual interconnected sections of a solid strip-like part, into which is respectively inserted a single recessed portion that surrounds the inner pipe. The inner pipe of the cooling pipe, which is embodied as a double pipe, is welded into the base of the supply chamber while the outer pipe of the double pipe is welded onto that part of the supply chamber that is disposed beyond the recessed portion. Also with this heat exchanger the connection to the reaction furnace is effected by means of an uncooled transition piece that contains heat-insulating material and is provided with a fork-shaped expansion. With this heat exchanger, each cooling pipe can be controlled individually and in a precise manner, and the supply chamber is rigid enough to withstand the high pressure of the coolant without additional reinforcements. A tangential supply of the coolant produces a rotating coolant flow, which ensures a good cooling of the base of the supply chamber and counteracts an undesired depositing of particles out of the coolant.
The object of the invention is to provide a connector having a high precision that can be subsequently installed in existing units on location with reduced expense between an uncooled cooling pipe of a reaction furnace and a cooled pipe of a reaction gas cooler.